The present disclosure relates generally to photodisruption induced by a pulsed laser beam and the location of the photodisruption so as to treat a material, such as a tissue of an eye. Although specific reference is made to cutting tissue for surgery such as eye surgery, embodiments as described herein can be used in many ways with many materials to treat one or more of many materials, such as cutting of optically transparent materials.
Cutting of materials can be done mechanically with chisels, knives, scalpels and other tools such as surgical tools. However, prior methods and apparatus of cutting can be less than desirable and provide less than ideal results in at least some instances. For example, at least some prior methods and apparatus for cutting materials such as tissues may provide a somewhat rougher surface than would be ideal. Pulsed lasers can be used to cut one or more of many materials and have been used for laser surgery to cut tissue.
The prior methods and apparatus to incise tissue with laser beams can be less than ideal in at least some instances. For example, the laser beam may incise tissue at a targeted location that is sub-optimal for a surgeon to further operate on.
An example of an eye surgery in which embodiments may be applied is described below. Cataract extraction is one of the most commonly performed surgical procedures in the world. A cataract is formed by opacification of the crystalline lens or its envelope—the lens capsule—of the eye. The cataract obstructs passage of light through the lens. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract the power of the lens may be increased, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those wavelengths are absorbed and scattered within the crystalline lens. Cataract formation typically progresses slowly resulting in progressive vision loss. Cataracts are potentially blinding if untreated.
A common cataract treatment involves replacing the opaque crystalline lens with an artificial intraocular lens (IOL). Presently, an estimated 15 million cataract surgeries per year are performed worldwide. The cataract treatment market is composed of various segments including intraocular lenses for implantation, viscoelastic polymers to facilitate surgical procedures, and disposable instrumentation including ultrasonic phacoemulsification tips, tubing, various knives, and forceps.
Presently, cataract surgery is typically performed using a technique termed phacoemulsification in which an ultrasonic tip and associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small (often round) hole is formed in the anterior side of the lens capsule. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure.
The lens may then be fragmented by segmenting and/or softening the lens by a laser to aid in removal by a phacoemulsification tip. Removal of the lens with the phacoemulsification tip is then performed through a primary corneal incision, for instance. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye. Typically, the IOL is held in place by the edges of the anterior capsule and the capsular bag. The IOL may also be held by the posterior capsule, either alone or in unison with the anterior capsule.
One of the most challenging and critical steps in the cataract extraction procedure is the extraction of the nucleus of the lens. After a primary incision is provided for insertion of the phaco tip, the surgeon generally first skewers a portion of the lens with the phaco tip. The portion of the lens attached to the phaco tip may then be pulled up and vacuum suctioned for removal. The remaining portion of the lens is rotated to align with the incision for the phaco tip to purchase. This process is repeated until the lens is fully extracted, and suffers from complications related to rotation, softening, and size of the lens.
First, the rotation of the lens by the surgeon may undesirably break up the lens, thereby complicating the lens removal process. Surgeons typically manipulate the phacoemulsification tip to rotate the lens nucleus to aid in efficient removal the lens nucleus. If the lens is fragmented in preparation for extraction, the surgeon typically first rotates the lens fragmentation pattern to align with the primary incision. This rotation may result in portions of the lens crumbling off as well as other damage. If this occurs, the surgeon must make additional attempts to find and acquire these smaller lens pieces, thus increasing the possibility of complications such as engagement with the posterior capsule.
Second, the large size of the removed lens pieces is cumbersome and places additional burden on surgeons. The standard capsulotomy is 5 millimeter in diameter, thereby providing an opening of about 2.5 millimeter for the phaco tip and portion of lens to be removed. However, the lens diameter is typically 8-10 millimeters such that even if the lens is segmented into four quadrants, the dimensions of the lens does not allow for easy removal through the phaco incision. Accordingly, the removal of the initial lens piece poses a particular challenge. Removal is even more difficult if the lens is not segmented, sculpted, debulked, and/or fully separated.
Third, lenses softened by a laser beam are harder to remove since softened lens pieces are more likely to fall apart, especially during extraction of the initial lens piece. Softened pieces are also more likely to crumble when rotated. The lens becomes thinned as pieces of a softened lens are broken off, with subsequent attempts at purchasing the lens being required.
In light of the above, it would be desirable to have an improved apparatus and method of treating materials with laser beams, such as the surgical cutting of tissue to treat cataracts and refractive errors of the eye. At least some of the above deficiencies of the prior methods and apparatus are overcome by the embodiments described herein.